Ann MacEwen, who has died aged 90, became perhaps the most distinguished female town planner of her generation, notably for addressing the relationship between people and cars. However, she is likely to be best remembered for her contribution to country life, as a guru of Britain's national parks.

The book National Parks: Conservation or Cosmetics? (1982), which she wrote with her second husband, the journalist Malcolm MacEwen, and its successor, Greenprints for the Countryside? (1987), gave the national parks movement an intellectual basis it had lacked. Without their influence, it is doubtful whether the national parks would have progressed, albeit hesitantly, from being mere romantic reservoirs of fine scenery towards becoming exemplars of how landscape and communities can be conserved.

Born Ann Radford (Anni to friends and family) in Sutton, Surrey, she was the grand-daughter on her father's side of the poets and writers Dollie and Ernest Radford, who first met in the British Museum Reading Room in 1880, did their courting in Karl Marx's sitting room and were comrades of William Morris. Her parents were doctors practising largely in working-class districts of north London. Ann was a third-generation socialist and became, like both her husbands, a member of the Communist party.

She was educated at Howell's school, Denbigh, north Wales, and took her diploma at the Architectural Association, then boiling with pro-gressive ideas, in 1940. There she met her first husband, John Wheeler, a gifted architect with whom she had two daughters. However, he was killed in an RAF test flight accident in September 1945. She worked for a couple of years with Geoffrey Jellicoe, later the doyen of landscape architecture, who was in charge of the Hemel Hempstead new town masterplan in Hertfordshire. (He offered her the job at a bus stop one morning, which she said favourably coloured her attitude to public transport for ever after.)

Ann had contracted polio as a child and walked with a limp. She married MacEwen, also widowed and then a Daily Worker journalist, in 1947. He had lost a leg in a motorcycle accident. As a good planner, she arranged to take a fast-track town-planning course to coincide with her third pregnancy and in 1949 got a job with the London county council (LCC). She worked on the redevelopment of the slums and bomb sites of Poplar and Stepney in east London. It was an exciting time for planners in London, but the money gradually dried up, and the parks, the health and social centres integral to Ann's plans did not materialise. She always regretted the rebarbative wastelands that marred her vision.

There was another problem. Ann's overwhelmingly male colleagues displayed little prejudice against her gender, but the LCC insisted that to qualify for pension and promotion, she must work full time, which included the Saturday mornings she devoted to her family. To get within head-banging range of the glass ceiling was difficult.

Malcolm and Ann broke with the Communist party when the Daily Worker refused to report the facts of the Soviet invasion of Hungary in 1956. Malcolm moved to the Architectural Journal, where, helped by Ann's professional know-how, he pioneered opposition to road-building and the motorised free-for-all. It was thus a natural progression for her to leave the LCC in 1961 and become the sole woman in Colin Buchanan's small team preparing the report Traffic in Towns for the Ministry of Transport in 1963. Although Ann would later acknowledge the shortcomings of the report, it marked a serious attempt to tackle the inhumanities of unrestrained and unplanned traffic. (Twenty years later she wrote with Joan Davidson The Livable City, a report condemned by a Thatcherite civil servant as "wringing wet".)

In 1964 Ann became a founding partner of Buchanan's consultancy in charge of a number of important studies for historic towns and cities. These were often battles against the macho road-based orthodoxy of traffic engineers, many of which she lost. At Edinburgh, she had a notable run-in with the city engineer who was infuriated by her opposition to his cherished motorway-sized bridge over the valley separating the old and new towns. He appealed to Buchanan to overrule her, but Ann, as ever calm, persistent and logical, won - to the city's lasting benefit.

In 1968 the MacEwens bought the Manor House at Wootton Courtenay in the Exmoor national park, where Ann created a welcoming and stimulating home. They explored the countryside on ponies which gave them, they said, eight sound legs instead of the two they had between them. Malcolm became a member of the park committee and, after a vicious contest, brought an end to the ploughing up of the remaining moorland, a battle that prompted their first book about national parks, their purposes and future.

National Parks: Conservation or Cosmetics? was published under the epigraph: "We each dedicate this book to the other, without whom it could not have been written." If readers were seduced by Malcolm's combative journalism, they were persuaded by Ann's rigorous arguments.

Malcolm suffered a series of strokes in the 1990s and Ann spent five or six years as his carer before his death in 1996, a muted and sombre end to their long, sparkling and productive partnership. Her three daughters, eight grandchildren and two great-grandchildren survive her.

· Ann Maitland MacEwen, town planner, born August 15 1918; died August 20 2008